${\mathrm{NH}}_3$ gas is liquefied more easily than ${\mathrm{N}}_2$ Hence

The constant "a" in Vander Wall's equation of state corrects for the intermolecular forces. The volume of one mole of atoms or molecules is the value of constant "b," which serves as a compensation for limited molecular size.

The value of "a" will be greater and the value of "b" will be less for a gas that is readily liquefiable.

As a result, it is stated in the question that NH₃ liquefies more easily than ${\mathrm{N}}_2$ and hence  $\left({\mathrm{NH}}_3\right)>a\left({\mathrm{N}}_2\right)$ but $\mathrm{b}\left({\mathrm{NH}}_3\right)<\mathrm{b}\left({\mathrm{N}}_2\right)$ 

Thus, the correct answer is C.